As shown in FIG. 1, a utility pole assembly 20 may be constructed with some or all components of the pole assembly 20 made from a composite material such as a fiberglass reinforced resin. The outer surface of the composite material is typically smooth so that animals may be discouraged from climbing the pole. Such a utility pole may not carry bacteria or generate slivers that can be dangerous to maintenance and repair personnel. The composite material may be a dielectric, which may reduce the amount of current that drains to the ground. The composite pole assembly may be immune to corrosive ambient conditions. The composite pole may be an alternative to wood utility poles that may require treatment with toxic chemicals to provide resistance to insects and fungi.
The pole assembly 20 illustrated in FIG. 1 includes a main pole member 22, a base member 24, and a top cap 26, shown in an exploded view so the parts are easily seen. Also shown is an exemplary cross arm 28 with insulators 30 supporting power lines 32. Of course the base and/or top cap may be of other configurations as desired.
Referring to FIG. 2, a generalized cross section of the main pole member 22 taken along line 2-2 of FIG. 1 may be seen. The cross section as shown in FIG. 2 is characterized as a hollow section formed by various geometric shapes, generally polygons. The outer periphery of the exemplary pole is octagonal, that is, the pole has eight substantially flat exterior surfaces. The eight sides of the external surface of the pole is a convenient number of sides, as it allows mounting of cross arms in a manner orthogonal to each other as well as at 45 degrees, which may accommodate requirements normally found in practice. A lesser or greater number of sides for the outer periphery of the pole may also be used if desired. Poles of lesser or greater numbers of sides may be fabricated in accordance with the present invention, though poles with not less than 6 sides or no more than 12 sides are preferred, poles with 8 sides being most preferable for fabrication, structural and other reasons. The sides may be of equal or unequal lengths. The angles between the sides may be identical or they may vary.
The internal periphery of the exemplary pole member 22 as shown in FIG. 2 may be defined by a plurality of flat regions 36 parallel to the flat sides 38 on the outer periphery of the pole, with the flat sides 36 being joined by circular arcs 40 tangent to adjacent flat regions 36 as disclosed in U.S. Pat. No. 6,453,635, which is assigned to the same owner as the present application. This internal periphery is referred to as a circular-tangere shaped inner channel. Circular-tangere shaped inner channels may be used with poles having other numbers of sides.
The pole may be formed by a pultrusion process using a fiber architecture of high strength filament thoroughly impregnated with a resin compressed and heated to form all or part of the pole structure. The filaments in the fiber architecture may be organized with orientations chosen to provide the desired mechanical properties for the finished pole. The filaments may be provided in various forms such as rovings that arrange all the filaments substantially parallel to each other along the length of the roving and fabrics that arrange the filaments at substantial angles to one another. Rovings are generally cordlike or ropelike arrangements of filaments. The term fabric includes mats in which the filaments are arrange randomly and stitched fabrics in which layers of filaments are joined together by stitching as well as woven and knitted fabrics. The rovings and fabrics may be arranged in layers to produce the fiber architecture for the desired pole structure.
FIG. 3 is a detailed cross-section of a corner portion of the generalized cross section shown in FIG. 2 for a prior art fiber architecture comprised of a number of layers. The layers comprise a surfacing veil 50, corner regions of longitudinal rovings 62, a fabric layer 52, a circumferential layer of longitudinal rovings 54, and another fabric layer 56 for the interior layer of the pole. The layers of the fiber architecture may be brought together in the desired arrangement by guides at the entrance of a pultrusion machine. The filaments of the fiber architecture may be thoroughly impregnated with a resin to bind the filaments together to produce a composite pole 22. As may be seen in FIG. 3, the corner regions of longitudinal rovings 62 are corner regions only, and form no part of the various layers in the flat regions between the corner regions of the fiber architecture.
The fabric regions 52, 56 may comprise fabric sheets that each individually circumscribe approximately one-half of the pole, two side by side sheets being used for each circumferential layer. Accordingly, each of the two fabric layers 52, 56 may have some form of discontinuity 180° apart. These discontinuities have been found to reduce the strength of the pole in bending about certain axes.
In a prior art fabric architecture, the cross-section may be formed as shown in FIG. 9, with an additional fabric strip 58 bridging the butt joint of the fabric sheets 52a, 52b that form the outer layer of fabric. The bridging fabric strip 58 may displace the adjacent roving 54 as suggested by FIG. 9, a bulge (not shown) may be created on the inner surface 36, or both effects may occur. In practice, the ideal joint illustrated in FIG. 9 can only be approximated. In particular, the edges of the fabric sheets 52a, 52b may overlap somewhat in some portions of the fabric architecture, which together with the fabric strip 58 immediately thereabove causes an unintended thickness of fabric in that area. Worse yet, in some regions of the fabric architecture there may in fact be a space between the edges of the fabric sheets 52a, 52b. This creates an even greater local weakness in the pole formed from the fabric architecture. FIG. 11 illustrates a similar intended butt joint in the inner layer of the fabric 56, specifically by way of a strip of fabric 60 adjacent to the butt joint of fabric sheets 56a, 56b that form the inner layer. This joint also is subject to the imperfections hereinbefore referred to, resulting in the reduction in the bending strength of the formed pole.